1. Field of the Invention
The present invention relates to catheters that have a deflectable portion. More particularly, the present invention relates to deflectable tip catheters that can be actively visualized and/or tracked in a magnetic resonance imaging (MRI) environment.
2. Discussion of the Related Art
Occlusive coronary artery disease results in myocardial infarction and deleterious left ventricular remodeling. Occlusive coronary artery disease can be treated. Treatment includes coronary balloon angioplasty, coronary artery stenting, and bypass graft surgery. However, due to the limited regenerative capacity of adult cardiomyocytes, ischemic events often result in irreversible cell injury and concurrent myocardial dysfunction, leading to congestive heart failure and death.
There is scientific evidence that delivering therapeutic agents, such as cells (e.g., stem cells), various genetic materials, growth factors, and the like, directly into the infarcted myocardial tissue may help to restore healthy tissue and normal myocardial function. Conventional interventional cardiology procedures, including the aforementioned treatments, such as balloon angioplasty, typically involve the use of a balloon catheter to dilate the occluded artery and X-ray fluoroscopy to assist the attending cardiologist guide the catheter. X-ray fluoroscopy, however, does not distinguish healthy from infarcted myocardial tissue, nor does it provide an anatomical image of the heart, where the ability to distinguish infarcted tissue from healthy tissue within an anatomical image of the heart is of vital importance to the cardiologist who is attempting to precisely deliver therapeutic agents using any one of the above-identified conventional techniques.
There are electro-anatomical mapping systems capable of providing a functional map of the cardiac anatomy; however, these systems cannot provide real-time images of the heart. An example is Biosense Webster's NOGA system, which is used in conjunction with X-ray fluoroscopy. The NOGA system employs a catheter comprising three coils and an endocardial potential measuring electrode located at the distal tip. During clinical use, three external magnets are placed at three different locations on the patient (e.g., under the patient's back and on the right and left side of the patient's chest). The cardiologist is then able to move the catheter around inside the left ventricle of the patient's heart, and, in doing so, the NOGA system measures the electrical activity at endocardial surface, as well as the motion and the location of the distal tip of the catheter. The NOGA system uses these measurements to create a three-dimensional, real-time, dynamic reconstruction of the ventricle, and assess the electrical and mechanical properties of the myocardium. The electrical potential and the motion of the ventricular wall are used, in turn, to differentiate between healthy, viable, tissue, and completely infarcted tissue. The primary drawback of this system is that it does not provide an anatomical image of the entire heart. It is therefore difficult to know the cardiac anatomy in which the catheter tip is located, and whether the catheter tip is apposed to the septum or the lateral wall. In addition, the procedure associated with the NOGA system is lengthy and the quality of the ventricle image is highly dependent on operator skill.
MRI is a diagnostic and imaging modality that is capable of providing a three-dimensional map, or image of the entire heart. Furthermore, MRI offers this capability without the ionizing radiation associated with other imaging modalities, such as X-ray fluoroscopy. MRI also provides real-time images with excellent tissue contrast; thus, the attending cardiologist can quickly and efficiently see the entire heart and clearly differentiate between healthy, viable, tissue and completely infarcted tissue. Ideally, MRI should be available to cardiologists for use during intervention therapy to accurately track and precisely guide the catheter to regions of infarcted myocardial tissue.
There are many types of injection catheters currently available; however, none is well suited for use in an MRI environment. For example, deflectable (i.e., steerable) tip catheters including multi-directional, bi-directional and uni-directional deflectable catheters are described in U.S. Pat. Nos. 5,487,757; 6,198,974; and 5,755,760, respectively. Injection catheters capable of delivering therapeutic agents to myocardial and other tissues are described, for example, in U.S. Pat. Nos. 5,980,516 and 6,004,295. Still further, deflectable injection type catheters are described, for example, in U.S. Pat. Nos. 6,346,099 and 6,210,362.
The various catheter designs described in the above-identified patents are not, as stated, well suited for use in an MRI environment for both procedural reasons as well as patient safety reasons. For instance, these catheters have ferromagnetic components that pose a safety hazard to the patient in a magnetic field environment, as they can cause injury to the patient, as they may move in an undesired manner due to the magnetic field. The ferromagnetic components can also cause image distortions, thereby compromising the effectiveness of the procedure. Still further, such catheters contain long metallic components, which can cause radiofrequency (RF) deposition in adjacent tissue and, in turn, tissue damage due to an extensive increase in temperature.
In addition, it would be difficult to track and/or visualize the location of the catheters described in the above-identified patents in an MRI environment. In general, there are two types of tracking in an MRI environment: active tracking and passive tracking Active tracking is the preferred methodology. It involves incorporating a transmit and/or receive antenna into the catheter design. Because a high intensity signal is transmitted or received, active tracking provides precise location information. An example of a catheter that can be actively tracked in an MRI environment is described in U.S. Pat. No. 5,928,145. In this patent, the catheter employs a loopless antenna. Another example of a catheter that can be actively tracked in an MRI environment is described in U.S. Pat. No. 5,699,801. In this patent, the catheter does not have a deflectable tip, nor is it capable of delivering therapeutic agents to a target location, nor is it capable of deploying other surgical instruments such as forceps during a biopsy procedure.
It would be very desirable to provide attending cardiologists with a catheter design that he or she can easily steer. In addition, it would be desirable provide a catheter that can be effectively tracked and/or visualized in an MRI environment, a catheter that is safe and effective when used in an MRI environment, a catheter that can be used to effectively deliver therapeutic agents to a target location within the patient using an injection needle, and deploy other surgical instruments such as a laser, a suturing device, forceps, a cauterization tool, and the like.